The transparency of glass or plastic, in the form of doors, windows, lenses, filters, display devices (e.g., display panels) of electronic equipment, and the like, can be impaired by glare or reflection of light. To reduce the amount of glare, for example, on plastic or glass, the surface typically includes a single layer of metal oxide (such as silicon dioxide), a metal fluoride, a metal nitride, a metal sulfide, or the like. Such coatings function as antireflective coatings.
Antireflective coated lenses represent a relatively small but rapidly growing segment of the ophthalmic lens market. These antireflective coated lenses are finding favor among consumers due to their enhanced cosmetic aspects and increased transmittance. Increased transmittance is of particular importance for applications such as night driving. Typically, antireflective ophthalmic lenses consist of a polycarbonate or other plastic base lens bearing a hard coat, with antireflective properties conferred by a multilayer stack of vacuum deposited metal oxides. The outermost layer in most antireflective stacks is silicon dioxide.
If left untreated, the high surface energy and porous structure of the antireflective stack render it easily contaminated and difficult to clean. Furthermore, the antireflective properties are extremely sensitive to and easily compromised by trace levels of organic contamination such as skin oils. Thus, the ophthalmic lens industry has developed a class of hydrophobic coatings that are applied to antireflective lenses in a final processing step.
Low molecular weight chloro- or alkoxy-functional alkylsilanes such as octyl- or perfluorooctylethylsilanes deposited from the vapor phase are commonly used in commercial hydrophobic coatings. Such films in the monolayer thickness range can effectively seal the surface and provide some antisoiling properties without interfering with the optical properties of the antireflective stack. The durability of these films, however, to dry rub abrasion is relatively poor, and the industry continues to search for a treatment with better initial oil and stain repellency. This problem has largely been addressed by a number of new antisoiling coatings comprising perfluoropolyether silanes.